Control device for hydraulic system



OcLS, 1963 PER OLLE LENNART GUSTAFSSON m m m m m 2 Sheets-Sheet l FiledNOV. 29. 1961 FIG.

Oct 8, 1963 PER oLLE LENNART Gus'rAFssoN 3,106,056

CONTROL DEVICE FOR HYDRAULIC SYSTEM Filed Nov. 29, 1961 2 Sheets-Sheet 2Z3 f 9,2% .\"N\ 35 FIG. 5 4Z ER OLLE LENWRT GUSMFSSON ATraRNEYs 4- y ZZINVENTOR.

United States Patent O 3,165,066 CONTROL DEVICE FR HYDRAULIC SYSTEM Per@lle Lennart Gustafsson, Karlskoga, Sweden, assigner The presentinvention relates to a control device for a hydraulic system of the kindincluding a pump for delivering a ow of pressure fluid at a constantrate of flow irrespective of the counterpressure acting upon the outputof the pump, one or several hydraulic motors connected to the ouput ofthe pump, an adjustable pressure reduction valve included in theconnection between the pump and each motor for reducing the pressure inthe connection and an adjustable relief valve also connected to saidconnection for limiting the Huid pressure therein to a maximum pressure.

FIG. l of the accompanying drawing shows schematically a conventionalhydraulic system of the general type above referred to. According toFIG. 1, the system comprises a storage tank 1 for the pressure fluidsuch as oil, a suitable pump 2 such as a gear pump, a relief valve 3which feeds oil back into the tank through a pipe 22 and may becontrolled by a spring, and a pipe 4 through which oil under pressure isfed to hydraulic motors 7 and 8. The connection between the pump and themotors includes pressure reduction valves 5 and 6 which serve to reducethe pressure of the oil fed to the motors to a suitable value. Therelief valve constitutes a safety valve which returns oil into tank 1when the pressure in pipe 4 exceeds the permissible maximum pressure.The reduction valves S and 6 are controlled by suitable spring means 9and I@ respectively and control the pressure of the oil delivered to themotors so that the pressure is always proportional to the load for whichspring means 9 and 19 are set. The setting of springs 9 and 1) may beadjusted by control levers 11 and 12 in a manner which is readilyapparent.

In order to assure that there is always an adequate working pressureavailable at motors 7 and S, the oil pressure in pipe 4 must beconstantly held somewhat greater than the maximum pressure for which thereduction valves 5 and 6 may be set. In actual practice the hydraulicmotors in such a system are set for a comparatively low pressure andwork with the maximum pressure only for short periods of time. As aresult the relief valve feeds oil back into the storage tank during mostof the time the system is operated and such a feed-back of oilrepresents a loss of energy which is at a maximum when the pressurerequired in the hydraulic motors is at a minimum. The energy lossmanifests itself in the form of an elevation of the temperature of thepressure fluid and such elevation in temperature may make it necessaryto include a cooling system in the installation.

It is the broad object of the present invention to provide in ahydraulic system of the general kind above referred to, a control deviceby means of which the aforeexplained energy loss is eliminated,completely or at least to a very substantial part.

In accordance with the invention the aforementioned object and otherobjects of the invention which will be brought out hereinafter areattained by controlling the relief valve and the reduction valves of thesystem by control means which always and automatically set the reliefvalve for a pressure that is somewhat higher than the highest workingpressure for which the reduction valves are set.

In the accompanying drawing a preferred embodiment of the invention isshown by way of illustration and not by way of limitation.

3,105,066 Patented Oct. 8, 1963 ICC In the drawing:

FIG. 2 is a diagrammatic view of a hydraulic system including a controldevice according to the invention.

FIG. 3 is a sectional structural view of the control device taken online III-III of FIG. 4.

FIG. 4 is a section taken on line IV-IV of FIG. 3, and

FIG. 5 is a perspective View of the control device according to FIGS. 3and 4.

Referring rst to FIG. 2 in detail, the hydraulic system according tothis gure is the same as that according to FIG. l, except that thesetting of the relief vvalve 3 is rst automatically and continuouslycorrelated with the setting of reduction valve 5 or 6. For this purposethe relief valve is provided with an adjustable compression spring 13and the aforementioned control levers 11 and 12 for the reduction valvesare extended beyond their fixed pivotal points 14 and 15 and theextended parts of the levers are hinged to links 16 and 17 respectivelywhich, in turn, are hinged to links 18 and 19 respectively. The links 18and 19 are pivotal about pivots 20 and 26a respectively and each of thelinks is coupled with the compression spring 13 so that it can vary theload of the spring Vwithin certain limits without affecting the settingof the other link. This is schematically indicated in FIG. 2 byelongated slots 40 through which links 1S and 19 respectively areextended.

As is evident, a pivoting of either lever 11 or lever 12 incounterclockwise direction will effect an increase in the compression ofspring 9 or 1i) and also of spring 13. As is also evident, actuation ofone lever, say lever 11, will not affect the setting of lever 12 andlink 19. In other words, the setting of one reduction valve for a higherpressure will not change the setting of the other reduction valve for alower pressure.

Turning now to FIGS. 3, 4 and 5, the control device according to thesefigures comprises a common housing or valve body 21 in which areaccommodated the relief valve and the two reduction valves. The pressurepipe and the pressure fluid return pipe are designated in FIGS. 2through 5 by the same numerals. Pipes 23 and 24 shown in FIG. 3 shouldbe visualized as being connected to motors 7 and 8 respectively.

Housing body 21 includes two perpendicularly shown ducts or bores 25 and26 and three horizontally shown ducts or bores 27, 2S and 29. The bores23 and 29 are connected by ducts or bores 30 and 31 with pipes 23 and24. In this connection it may be pointed out that in FIG. 3 theuppermost circle represents the relief valve and the lower circlesrepresent the two reduction valves. A plunger 32 is slidable in bore 27and a plunger 33 is slidable in bore 29. A similar plunger should bevisualized as being slidable in bore 2S. Each of the valve plungerscomprises two cylindrical portions 32a and 33a respectively, the outerdiameter of which just ts the inner diameter of bores 27 and 29respectively and set-off joining portions 32b and 33h respectively. Eachplunger is formed in its periphery with a channel 32a and 33erespectively which leads from the reduced joining portion of the plungerto the lefthand end surface thereof.

The plungers may be urged towards the left by means of push rods 34 and35 which act upon springs 36 and 37. The push rods in turn may be movedtowards the left through equal distances by means of a common controlmember 38 which should be visualized as being controlled in any suitablemanner. In this connection it may be mentioned that there is shown inFIG. 4 the control of the relief valve and one of the reduction valvesonly. The control of the second reduction valve should be visualized asbeing effected in the same manner.

As has been previously explained, the concept of the invention requiresthat the relief valve is set for a pressure that is somewhat higher thanthe pressure for which the reduction valves are set. This is effected inFIG. 4 by showing spring 36 somewhat heavier than spring 37. The sarneeffect can be obtained by using springs of equal strength and fitting aspring washer in the holder for spring 36. It is also possible to effecta differential in the setting by springs of equal strength but plungersof diiferent diameters. Which one of the aforementioned possibilities ofobtaining the same result is adopted is not a matter of principle but ofconvenience of manufacture.

The control device as hereinbefore described functions as follows:

In the position shown in FIG. 4 oil can freely pass through bores 25, 27and 26 to be returned into the storage tank l by pipe 22. As isapparent, the flow of oil through the device is very little restrictedso that no substantial oil pressure will be built up in the system.

When now the control member 33 is moved towards the left the plungers 32and 33 will also be moved towards the left as a result of the increaseof the load at springs 36 and 37. Due to the displacement of theplungers toward the left, shoulder 39 of plunger 32 will move closer tothe respective peripheral edge of housing 2l thereby correspondinglyconstricting the ow of oil from bore 27 into bore 26. As a result, thepressure in bore 27 will correspondingly rise and such increase inpressure will force oil through channel 32e into the portion of 27closed off by the respective plunger portion 32a. This increase ofpressure urges plunger 32 towards the right and into a position in whichthe oil pressure and the pressure exerted by spring 36 upon the plungerare in balance. T he pressure in pipe d and bores 25 and 27 willgenerally be proportional to the distance by which push rod 34 has beenmoved towards the left.

Plunger 33 has two shoulders 4l) and 4l which are longitudinally spacedso that in the illustrated position shoulder 4t! closes the connectionbetween bore 25 and bore 29 and opens the connection between bore 29 andbore 26. When now plunger 33 is moved towards the left as previouslydescribed, shoulder 40 will open the connection between bore 25 and bore29 and shoulder 4l will close the connection between bore 29 and bore26. As a result the pressure in bore 29 rises and causes a ow of oilthrough channel 33C. T he increase in pressure in the portion of bore 29closed by the left-hand plunger portion 33a urges plunger 33 towards theright until the plunger occupies a position in which the oil pressureand the pressure of spring 37 are in balance.

As is now evident, a displacement of control member 38 effects asimultaneous change in the setting of the relief valve and therespective reduction valve, though for different pressures due to thedifference in the strength of springs 36 and 37.

Turning now to FIG. 5, this figure shows that control member 38 occupiesonly about half of the face of pushrod 34. This permits the use of asecond control member for simultaneous control of the relief valve andthe second reduction valve. FIG. 5 shows a push-rod 42, corresponding infunction to push-rod 35, for control of the second reduction valve.

`While the invention has been described in detail with respect to acertain now preferred example and embodiment of the invention, it willbe understood by those skilled in the art, after understanding theinvention, that various changes and modifications may be made withoutdeparting from the spirit and scope of the invention, and it is intendedtherefore to cover all such changes and modiiications in the appendedclaim.

What is claimed as new and desired to be secured by Letters Patent is:

A control device for a hydraulic system including a pump for pumpingpressure fluid at a constant rate of flow, a hydraulic motor connectedto the output of said pump, an adjustable pressure reduction valveincluded in the connection between the pump and the motor for reducingthe pressure in said connection and an adjustable relief valve alsoconnected to said connection for limiting the uid pressure therein to amaximum pressure, said control device comprising common control meansfor said reduction valve and said relief valve to vary the fluidpressure control effected by said valves, said control means includingfirst transmission means connected to the relief valve and secondtransmission means connected to the reduction valve, the ratio oftransmission of said transmission means being such that the relief valveis set for a higher pressure than the reduction valve in response to anygiven setting of the control means, each of said transmission meansincluding a cylindrical duct, a plunger slidable in said duct, a springmeans acting on one side of the plunger to urge the same in onedirection, a duct feeding pressure iiuid into the duct portion on theother side of the plunger to urge the same in the opposite direction,the cylindrical duct of the iirst transmission means cornmunicating withthe relief valve and the cylindrical duct of the second transmissionmeans communicating with the reduction valve, the position of theplungers in the ducts controlling the fluid pressure at the relief valveand the reduction valve respectively and being controlled by the springpressure exerted on said one side of the plunger, the spring pressureexerted upon the plunger associated with the first transmission meansbeing stronger than the pressure exerted upon the plunger associatedwith the second transmission means in response to the setting of thecontrol means.

Talak Dec. 10, i957 Malt...

